Telephone system



W. L. DODGE.

TELEPHONE SYSTEM.

APPLICATION FILED SEPT-22, I9l9- Patented Oct. 11, 1921.

2 SHEETS-SHEET I- W. L. DODGE.

TELEPHONE SYSTEM.

APPLICATION FILED SEPT.22. 1919.

\A 6 55% v L" u n m 7 w W n 1m t u 6 0 A m m W 5 A .W /.m a a P UNITED STATES PATENT OFFICE.

WILLIAM L. DODGE, OF MAPLEWOOD, NEW JERSEY, ASSIGNOR T0 WESTERN ELEC- TRIO COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

TELEPHONE SYSTEM.

Application filed September 22, 1919.

To all whom ii may concern Be it known that I, \VILLIAM L. Donor, a citizen of the United States. residing at Maplewood, in the county of Essex. State of New Jersey, have invented certain new and useful Improvements in Telephone Sys terns, of which the following is a full, clear, concise, and exact description.

This invention relates to telephone systems and more particularly to such systems in which the signals for a plurality of trunk lines extending between stations or central oliices are controlled over a single signaling path common to such trunk lines and likewise extending between the two stations.

An object of this invention is the provision of improved signaling means for terns of this character.

In attaining this object of the invention there is provided at each end of the common signaling path an intermittently opersting commutator or distributer for indi vidually associating the trunk lines with the common signaling path and for transmitting and receiving thereover code combinations or code signals individual to the various trunk lines, the code of which is determined by an intermittently operating selector switch controlled by the individual trunk lines and controlling the polarity or" 'naling current connected with the send- 7. segments of the sending distributor which control the selection of the trunk line at the receiving end, and a pole changing switch individual to and controlled by each trunk line for determining the polarity of signaling current connected with another of the sending segments of the sending distributor for the purpose oi": determining the of the selected trunk line to be operated.

A further object of this invention concerns means provided for testing the signaling portion of such telephone systems and the associated. apparatus controlling the transmission of code signals over the common signaling path.

In attaining this second object of the present invention, switching apparatus normally connecting the signaling path and the signal control apparatus thereof with signal control leads individual to and associated Specification of Letters Patent.

Patented Oct. 11, 1921.

Serial No. 325,518.

with the various trunk lines and normally connecting a duplicate signaling path and associated signal control apparatus with testing equipment comprising testing keys, signals and controlling relays, when actuated simultaneously disconnects the individual signal control leads from the first and connects these leads with the second common signaling path and associated signal control apparatus, and disconnects the testing equipment from the second and connects it with the first signaling apparatus and associated signal control apparatus, whereby the signals for the trunk lines may be transmitted over the second or duplicate signaling path, while the first signaling path and associated signal control apparatus are being tested.

A still further object of this invention is the provision of means for determining whether the signal sending and signal receiving distributors at the opposite ends of the common signaling path are operating in synchronisin.

For a more complete understanding of this invention reference should be had to the following description considered in connection with the accompanying drawings, in which Figures 1 and 2 when placed end to end with Fig. 1 to the left of Fig. 2 illustrate one embodiment thereof. For convenience, where like apparatus is employed at oiiiccs X and Y, it will be designated by the same reference characters, that at office X without, and that at oflice Y with primes.

Referring to the drawings, there is shown a cord circuit F located at an otlice X for establishing connections with a trunk line L2 extending from the oilice X to the office Y. The trunk line L2 may be connected with a telephone line G terminating at the oilice Y. lVhile but one trunk line L2 is shown it is to be understood that this is for the purpose of convenience only and that this invention contemplates a plurality of such trunk lines.

To provide for the transmission of super visory and other signals between operators and between operators and subscribers in connection with the establishment of connections over the various trunk lines, a signal receiving distributer RD, holds open its contact which is in the locking circuits ol locking relays Gl to (36' inclusive, whose energizing windings are connected with the respective individual receiving segn'ients l to 6 inclusive of the receiving distributer lil Relays 61 to 61- inclusive control relays 67 to 81' inclusive comprising the pyramid selecting relay combination which coi'iperates with locking relay to select the signal receiving conductors ll terminating in contacts of relays T l to 81 inclusive. Locking relay (36 controls the polarity of signaling current connected with the selected signal receiving conductor or lead for determining the signal to be operated.

For transmitting over the common signaling path P signals originating at he ollice Y, sending equipment comprising a sending distributer selector switch and associated control apparatus and signal control leads similar to taat described in connection with the otlice X is provided at the oliice Y. This apparatus, for purpose of convenience is represented by the dotted 'ectanglc desig nated SE. Likewise, in order that the code signals transmitted from the ollice Y to the oil'ice X over the common signaling path P may be properly received and translated and the appropriate trunk lines selector there is provided at this otlice X receiving equipment comprising receiving distrihuter RD, pyramid selecting relay combination, control locking relays and signal receiving leads such as was described in connection with the oilice Y. This receiving eouipinent at the oilice X, for the purposes convenience, is represented by the dotted rectangle As shown in the drawings, a duplicate common signaling path Di extends between the two oilices. For transmitting and receiving over this duplicate common signaling path DP code signals resulting from signals originating at either of the oliices there is associated with tnis duplicate common signaling path DP sending and receiving equipment located at each of the offices. lhe sending and receiving equipment for this duplicate signaling path located atthe otiice X is indicated by the dotted rectangles USE and DRE, and that located at the otfice Y is indicated by the dotted rectangles DEE and DRE.

In order that the common signaling paths and the associated sending and receiving distributers may he tested. there is provided testing equipment which may be associated with either of the signaling paths. i por tion of this testing equipment is individual to the trunk lines while another portion is common thereto. Since the testing equipment located at the two ollices is identical, that located at the office X will be described, while that located at the ofiice Y will not be of switches. while the individual trunk line is associated with the signal control apparatus of the signaling path P through normally closed contacts otf similar switches. These switches at the ollice X for the trunk line L2 are shown within the dotted rectangle K2. Those in the upper row control the connection and disconnection of the trunk lines with the signaling paths, while those in the lower row control the connection of the testing equipment with the signaling paths. tiimilarly arranged switches for the trunk line L2 and serving the same purposes at the ofiice Y are shown within the dotted ree tangle 1C2.

liaving in mind this brief description of the invention shown in the drawings, it is thought that the invention will be thorougyhly understood from a description of the operation of the system shown. First, the setting up and breaking down of a connection between. the cord circuit F and the telephone line G will he described, and next the testing): of the signaling system will be described.

(omicci'ioa of 00rd circuit F with trunk Zinc HZ.

The operator at the ollice X, desiring to estab sh c-c '..ection witl the telephone l1ne it the ollice X, communicates tcriniuati with the operator at ollice Y over an order wire (not shown).

The operator at the o'f certaining from the operator at the r Y that the connection with the telenc line to be completed by way of no trunk line L2. inserts calling plug 20 ot the cord circuit F into jack 21 ot the and the contact of relay 22 to ground. Upon the operation of reh 911:, relay 25 operates over a circuit from battery, through a middle alternate contact of relay 2%, resistance 26 and winding oi relay to groun 1. Relay 25 thereupon locks up through its left-hand alternate contact, resistance 26 and its own wmding; to ground. The operation of relay also connects positive signaling battery with the signal control lead C2 and connects the signal control lead i with one terminal of the winding; of relay 2:. The operation of relay 25 grounds the signal control lead A2 and the common start lead ST.

Upon the grounding of the common start lei d ST, start magnet. associated with the automatic sclctor switch H operates over a circuit from battery through the winilinui of mz'ignet 28, the start lead ST, a norm l contact 01' the switch K, right-hand contact of relay 30, right-hand alternate contact of relay and a normal contact ol? relay to ground. Start magnet 28 upon being energized completes acircuit for the motor magnet UM which thereupon interrupts it" own circuit rotating the brushes of he selector switch step-by-step until the brush a engages the contact to which the signal control lead A2 is connected, whereupon relay 55 operates over a circuit from battery through the le"l thand winding of relay brush a, a normal conta t oi switch K, signal control lead A2, middle contact of r' lay 30, miodle alternate contact of relay 25 and a normal contact of relay 2'? to ground. \Vith the brushes of the automatic selector switch H stopped in engagementwith the contacts allotted to trunk line L2, the brushes 1 to 6 inclusive connect positive sip,-- naling current with the lust, third, fourth and sixth sending segments of the sending distributor TD and negative signaling current with the second and iii'th sending;- segniients therol. Relay in operating imn' ediately locks up over a circuit- :.trom hattery through its right-hand winding and left-hand alterna e contac and the contact of release relay 3'7 to ground. Relay in operating also opens its normal contact, thereby stopping the operation of the motor magnet hfilil and closes its middle alternate contact, thereby ca using the operation of relay 27 over a circuit from battery through a middle alternate contact oi? relay 2st, lelithand contact of relay 30, winding; of relay 27, right-hand alternate contact olf relay id, ri 'nal control lead B23, :1 normal contact of the switch K, brush 7) of the selector switch H, middle alter ate contact of relay 35, normal contact of relay 39 and the normal contact of release relay 37 to ground. Relay 2'? in operating locks up over a circuitfrom battery through a middle alternate contact tie winding and alternate mute t of relay 21 to ground. llelay i7 in'opcratincg' opens its normal contacts, tlerchy remoi'u' the ground xii lead 5-1. and

si 'nal control lead Iii. th one cults of start magnet thcreh opened. Rel

leases its armat serves to switch H from the associat- .H Minus 1:)

the selector ed with any other which it is common.

r ng now W closure or me ontac of this relay ca oi? release n'iagruei; "llllf rilu'itcr Ti) over M hand a lteri role;

armature releases the crush 1 ing distributor i a "omplete l'Q'x'th tilt Upon engragcmein the startiinr segment a. connected with the 1 thereby causing the differential polarizcd ma is the brush arm m ment with the segment *elcasc may not TDM is deonergized, rest-o fl 1" it a mature to normal. position for engag st pping the brush arm at the co ici complete cycle. The cngz agijcmcn brush arm with the segmen operation of a slow role so rel circuit from battery through the chrush arm, segmen i) and the i l slow release relay 39 to ground This siay R9 thereupon removes round from the lirush t) 01? the automatic selector switch ll. As the brush arm succc ilTOlfj engages ll 0 individual sending segments 1 to {3, sig naL ing current oi? the pola r ,ics connected with iii) sling; path :iltlOll of the at he olli :e

t n ing of these segments are succ" sir-sly connected with too common signaling 33' h P which to minates on the common pending ring Tl polarities are such that the sending iilistrihuter TD transmits a coded signal comprising six impulses. the first, third, fourth and sixth of which are positive and the second and fifth are negative. ll hen the brush arm moves out of cu emcnt lease relay 37 to ground. The energization of release relay 37 opens the locking circuit of relay 35, which thereupon releases. Relay 39 is made slow in releasing so that its contact remains open until after the opening of the contact of the release relay 3?. As the brush arm moves out of engagement with segment ll, release relay 3''? is dei'energized. When the brush arm engages segment *1, negative signaling current is connected with the common signaling path P. The automatic engagement selector switch H is now in condition to be seized by another trunk line, since trunk line L2- is disconnected therefrom, and the sending utcr TD is in normal condition.

Upon the operation of the difi'erential polarized relay due to the transmission of the first positive or starting impulse over the common signaling path P when the brush arm engages the starting segment .9, release magnet RDM of the receiving distributer RD is energized over a circuit from battery through the alternate contact of the ditlerential polarized relay 50, segment 51, the brush arm, segment 53 and the winding of release nuignet RDM to ground. The attration of the armature of the release magnet RDU upon the energination thereof releases the brush arm of the receiving distributer ED which is thereupon rotated through a complete cycle at the end of which the brush is stopped in its normal position. As the brush arm moves out of engagement with the segments 51 and 53 the release magnet RDH is de'e'nergized permitting the release of its armature preparatory to stopping the brush arm when it reaches its normal position. When the brush arm moves out of engagement with the segment 55, relay 58 is dee'nergized closing its contact which is common to the locking circuits of relays 61 to 66 inclusive. The armature ot' the differential polarized relay 50 remains in its normal position when negative signaling current is conneted with the other end of the common signaling path P and moves to its alternate position whenever positive signaling current is connected with the other end of the common signaling path P. Th brush arms of the sending and receiving distributers TD and RD are being rotated at the same time and in synchronism. Therefore, when the brush arm of the sending distributer TD engages sending segments 2 and 5 to which negative signaling current is connected, the armature ot' the differential polarized relay 50' is in its normal position while the brush arm of the receiving distributer RD engages the receiving segments 2 and 5. Thereforerelays 62 and 65 are energized, the former over a circuit from battery through the normal contact of relay 50, common redistrib- I ceiving ring 54, the brush arm, receiving segment 2 and the lower winding of relay 62' to ground while relay 65' is energized over a similar circuit except that receiving segment 5 instead of 2 is included in its circuit. Relays 62 and 65 immediately lock up through their respective upper windings and alternate contacts and the contact of relay 58 to ground. Relay (32 in operating causes the encrgization of relays to 73 inclusive, of the pyramid selecting relay combination over a circuit from battery through the windings of these relays in series, upper normal contact of relay 89, and the lower contact of relay 62 to ground. When the brush arm of the receiving distributor RD engages segments 56 and 57, signal receiving relay 85 operates over a circuit from negative signaling battery through the middle normal contact of relay 86, normal contact of relay 66, lower normal contact oi": relay 86, segment 56, the brush arm, segment 57, lower normal contact of relay 8?, lower alternate contact of relay 65, the upper normal contact of relay 87, the lower normal contacts of relays 67 and 69, lower alternate contact of relay 73, upper normal contact of relay 81, a normal contact of switch K, signal receiving lead E2 and the right-hand winding of signal receiving relay 85 to ground. Signal receiving relay 85 thereupon completes a locking circuit for itself from battery through its alternate contact and left-hand winding to ground, and causes the lighting of supervisory lamp 90 over a circuit from battery through the alternate contact of signal receiving relay 85, lower normal contact of p relay 91 and the lamp 90 to ground. The operation of signal receiving relay also causes the energization of slow release relay 98 over a circuit from battery through the alternate contact of signal receiving relay 85, the normal contact of signal receiving relay lO-l and the winding of relay 98 to ground. lVhile signal receiving relay 104 is also energized in parallel with relay 85, it does not lock up for slow release relay 98 is not energized and relay 104 therefore performs no useful function at this time. The lighting of this lamp is an indication to the operator at the office Y that connection has been made with the proper trunk line L2 by the operator at the ottice X and is what is usually known asa guard signal. hen the brush arm moves out of engagement with the segments 56 and 57, the energizing circuits of relays S5 and 10l are opened causing the deiinergization of relay 104: before slow release relay 98 closes its contact. \Vhen the brush arm engages the segments 51 and 53, the armature of relay 50 is in its normal position since the brush arm of the sending distributor TD is in engagement with segment 7 thereof and negative signaling current is connected with the common signaling path P, and the energizing circuit of the release magnet RDM is open. The engagement of the brush arm with the segment 55' causes the energization oi the relay 58', which thereupon opens the hickii-ig circuits of relays 6:2 and liclays to 73, inclusive, are thereby deene gi'zed restoring the pyramid electing: relay combination to normal condition.

(I'on'iiect z'oa of trim/0 line Z2 with telepizmm Zine (3.

Upon observing the lighted condition all the lamp 1)!) the operator at the ollice Y inserts plug 92 of the trunk line L2 into jack 9?) of the telephone line (1 causing the operation of relay 91 over a ci'cuit from battery through the winding of relay 91 sleeve contacts ot the plug )2 and jack 93 and the winding of cut-off relay 9:2; to ground. Relay 91 in operating opens the circuit of and cxtinguishes the lamp 90. This relay 9], in closing its n'iiddle alternate contact, causes the operation oi? relay 24: over a circuit from battery through the normal. contact or relay 25. winding of relay -24, contact of supervisory relay )5 and the middle alternate contact of relay 9 1. to ground. Relay 24: in operating locks up over a circuit from battery through a, middle alternate contact and its winding, the contact of supervisory relay 95 and the mid-- dle alternate contact of relay )1 to ground. Relay 25' thereupon operates over a circuit from battery through a middle alternate contact of relay Qt. resistance 26. and the Winding of relay to ground. This relay 25', upon being energized, locks up over a circuit from battery through its left-hand alternate contact. resistance 26 and its own Winding to ground. Relay 2i in operating connects positive battery with the signal control lead 0'2, connects signal control. lead BQ with one terminal of the winding of relay 2?, While relay 25' in operating grounds the signal control lead AQ and the common start lead ST. This start lead and the signal control leads are associated with an automatic selector switch H which controls the polarities connected with the sending segments of sending distributor T D at the office Y. The automatic selector switch H and the sending distrilniter TD of the sending equipment SE and the associated control apparatus thereof thereupon. function in exactly the same manner as described in connectionwith selector switch H and the sending distributor Tl.) to determine the code or and to transmit the coded signal over the common signaling path I. The code signal transmitted by the sending distributer TD is the same as that transanal transmitted over the common signaling path fl. from 'llll oilice Y upon ceivcd at the ollice .auses the dil l polarized relay all in lilllllllOll in same manner as i ircviously descri uzd in connection with relay fill. The receiving Kributcr lll). local coalrol ap airatus therein", locking relays l3! and on, and pyramid l -ctin; relays ill to T3 inchiisive ot the receiving iapiipnieut llll controlled by the relay on then function to select signal receiving lead E2 and to transmit i'liercover an impulse l'rorn negative signaling battery. This negative impulse traverses the leit hand or energizing winding oif siunal. receivingj relay 100. which is thereiiiy encriZiI le l and locks up over a cir uit from battery through the right-hand mntact and winding thereof and the contact o'l relay 22 to ground. l pon the cessation oi. this nega tive impulse and the stoppino' ot the brush arm of ihe receiving distli'inuter RD, all. amniralus oi the receiving equipment RE is restored to normal condition ready to receive any other code signal and translate it into the apprcmrintc signal of the proper trunk line. Signal receiving relay 100, upon being energized, closes its letthan 'l contact connecting resistance 91) in parallel with the winding: ol relay 22, thereby reducing the resistance in circuit with supervisory lamp This supervisory lamp is thereby lighted and now serves as a signal to the operator at the ollice X that connection has been cstab shod with the telephone line G and that the circuit is in condition l'or signaling the Station on the connected telephone line G.

(hi/auto," at office X acme-ms ringing 70 2/.

Opera/tor (/5 office X restores fang ling 1 66?].

Upon the restoration of the ringing key 101 to normal position, relay 102 releases its armature whereupon relay 30 is de'e'ncrgized closing its contacts. The closure of the right-hand and middle contacts of the relay grounds the signal control lead A2 and the common start lead ST. The selector switch H and the sending distributer TD now function to transmit the same code signal transmit-ted when the cord circuit F was connected with trunk line L2, as previously described. During this operation, relay 2? is energized over signal control lead 132 and locks up removing ground from signal control lead A2 and the start lead ST. At the conclusion of the transmission of the code signal, the control apparatus of the selector switch H, and the sending distributer TD are restored to normal condition ready for use by any other trunk line initiating a signal at the office X. This transmittal code signal being received at the office Y causes the receiving distributer RD locking relays and pyramid selecting relays to function to select signal receiving lead EQ and to transmit thercover a negative impulse, after which this receiving equipment is restored to normal condition. This negative impulse over signal receiving lead E2 traverses the energizing or right-hand winding of signal reeiving relay 10-l, which energizes, and then holds up over a circuit from battery through its left-hand winding and contact and the contact of slow release relay 98 to ground. The closure of the ri ht-hand alternate contact of signal receiving relay 10st causes the cnergization of slow release relay 105 over a circuit from battery through the alternate contact of signal receiving relay 85, right-hand alternate contact of signal receiving relay 104: and winding of relay 105 to ground. Relay 105 upon being energized, causes the energization of ringing relay 106. Upon the opening of the normal contact of signal receiving relay 10a, the energizing circuit of slow release relay 98 is opened so that this relay in1- mediately begins to release its armature. Upon the full release of the slow release relay 98 the holding circuit of signal receiving relay 10c is opened causing the release thereof. Signaling receiving relay 10-l in releasing its armatures opens the energizing circuit of slow release relay 105, which, when fully released, opens the energizing circuit of ringing relay 106. This combination of slow release relays controlling and controlled by the signal receiving relay 101 determines the length of time that the ringing relay 106 is energized and therefore the length of time that ringing current is connected with the telephone line G. During the energization of ringing relay 106, a source of ringing current 107 is connected with the called telephone line G to cause the operation of the usual call bell at the station thereon (not shown).

Subscriber of telephone line G removes rcccwcr from switchlioolc.

The subscriber at the station on telephone line G in responding to the operation of the call bell thcreat removes the receiver from the switchhook, thereby causing the operation of supervisory relay 95 which opens the locking circuit of relay 2%. Relay 21 in releasing its armature connects negative signaling battery with signal control lead C? which is connected through a normal contact of the switch K with the allotted contact on the sixth level of the selector H of the sending equipment SE. The opening of the middle alternate contacts of relay 24- opens the locking circuit for relay 2? which thereupon releases its armatures, grounding the signal control lead AQ and the common start lead ST. The selector switch H and the sending distributer TD of the sending equipment thereupon function to determine and transmit a coded signal over the common signaling path P to the ofiice X. During this operation the signal control lead B2 is temporarily grounded, short-circuiting the winding of relay 25. Relay 25 thereby deenergized, releasing its armatures removing ground from the signal control lead AQ and the common start lead ST. Relays 24c, 25 and 26 are now d-eenergized, and upon the conclusion of the transmission of the coded signal, the control apparatus of the selector switch H, and the sending distributer TD of the sending equipment SE are in normal position ready for use by any other trunk line initiating a signal at the oflice Y. The transmitted code signal comprises six impulses, the first. third and fourth of which are positive and the second, fifth and sixth are negative.

This code signal being received at the otlice X, the receiving distributer RD in cooperation with relay 50 causes the energization and locking up of locking relays 62, G5 and (3", the first two of which cause the pyramid selecting relays of the receiving equipment RE to select the signal receiving lead E2, and the third of which, relay 66, in cooperation with the receiving distributer RD, connects with and transmits over this selected signal receiving lead E2 an impulse of positive signaling current. This positive impulse traverses the left-hand winding of signal receiving relay 100. The signal re ceiving relay 100 is locked up at this time. The windings of this relay are so related that with the relay locked up when a positive impulse is transmitted through its lefthand winding the relay is rendered differential and releases its armatures. The release of the signal receiving relay 100 disconnects the resistance 99 from parallel 85, duecto a 1 positive impulse traversing its right-handwinding, causes supervisory lamp ,90 to be lighted over a circuit from battery throughthe normal contact of signal receiving relay 85, the lower alternate contact of relay 91 and the lamp 90 to ground. The lighting of this lamp 90 serves as a disconnect signal to the operator at the oflice Y. The opening of the alternate contact of signal receiving relay 85 causes the deenergizationof slow release relay 9S. lVhile signal receiving relay 101 is energized, due to the positive impulse traversing its righthand winding, this relay is rendered differential immediately upon the closure of its left-hand contact and is thereupon de energized. Consequently, the energization of a signal receiving-relay 104: at this time performs no useful function. Upon the return of the brush arm of distributer RD to normal position, relay 58 is energized opening the locking circuits of and deenergizing the locking relay 62, 65 and 66. The deie'nergization of locking relay 62 causes the denergization of pyramid selecting relays to 73 inclusive. All apparatus for thereceiving equipment is therefore now in normal condition ready for receiving any further code signals transmitted over the common signaling path P.

Operator at 0 7555 Y disconnects tmmlc Zine L% from telephone Zine G,

The operator at the office Y upon observing the lighted condition of the supervisory lamp 90 may withdraw the pl11g192 of trunk line L2 from the jack 93 of the telephone line G, whereupon relay 91 and cutoff relay 94 release their armatures. The release of relay 91 opens the circuit of and extinguishes supervisory lamp 90. The opening of the middle alternate contact of relay 91 causes the deenergization of relays 2-1 and 27. Negative signaling current is thereupon connected with signal control leads CQ, and start lead ST and signal control lead A 2 are grounded.

The automatic selector switch H and the sending distributer TD of the sending equipment SE thereupon function to determine and transmit over the common signaling path P, a code signal of six impulses, the first, third and fourth of which are positive, and the second. fifth and sixth of whichare negative. Upon the termination of this code signal, signal control lead 132 is grounded in the manner hereinbefore described and short-circuits the winding of relay 25. Relay 25 is thereby denergized and releases'its armatures, removing ground from the start lead ST and the signal control lead AQ. At the conclusion of the transmission of the coded signal all apparatus of the sending equipment SE is restored to normal condition.

Upon the reception of the transmitted code signal at the ofiice X differentially polarized relay 5O cooperates with the receiving equipment RE to select the signal receiving lead E2 and to transmit thereover positive impulse which traversesthe lefthand winding of the signal receiving relay 100. Sincethelocking circuit of this signal receiving relay 100 is open at the con- I tact of relay 22, the energization thereof at this time performs no useful purpose.

The operationsdescribed above with reference to building up a connection over the trunk line L2'with the telephone line G and the breaking down of such a connection are characteristic of those taking place in build ing up and breaking down a connection over any one of the trunk lines to which the signaling path P is common. The only essential ditl'e'rence in operation, so far as the establishment of connections over the different trunk lines is concerned, is that different code signals are employed for the different trunk lines, and while this invention is not limited to any particular arrangement of code signals, the codes shown in the following table have been found to be very satisfactory for a total of thirty-two trunk lines served by the same common signaling path.

Si nals from ofllce S1gna1s from oifice X to oflice Y. to 0mm XI Trunk Discon- Receiver Receiver Guard" Ring nect. on hook. 011 hook.

1 3 3 36 3 36 2 25 25 256 25 256 3 4 4 46 4 46 4 5 5 56 5 56 5 34 34 346 .34 346 6 35 35 356 35 356 7 45 45 456 45 456 s 345 345 3456 345 3456 9 2 2 26 2 26 10 23 23 236 23 236 11 24 24 246 24 246 12 234 234 2346 234 2346 13 235 235 2356 235 2356 14 245 245 2456 245 2456 15 2345 2345 23456 2345 23456 16 1 1 16 1 16 17 12 12 126 12 126 is 13 13 136 13 136 19 14 14 146 14 146 26 15 15 156 15 156 21 123 123 1236 123 1236 22 124 124 1246 124 2 1246 23 125 125 1256 125 1256 24 134 134 1346 134 1346 25 135 135 1356 135 1356 26 145 145 1456 145 1456 27 1235 1235 12356 1235 12356 23 1245 1245 12456 1245 12456 26 1345 1345 13456 1345 13456 30 1234 1234 12346 1234 12346 31 12345 12345 123456 12345 123456 32 0 o 0 In tl11s table, the numbers in the first column indicate the numbers asslgned to the trunk lines, while the numbers in the remaining columns indicate the order of the negative impulses in each group of six. The number 0 appearing in the last line in the second, third and fifth columns of the table means that no negative impulses are transmitted. The various code signals represented in the table are determined by the polarities connected with the contacts of the first to sixth levels of the automatic selector switches H and H, the polarity connected with the contacts of the sixth levels being further determined by the position of the pole changing relays 24 and 24' of the various trunk lines.

Testing equipment and operation.

Referring now to the testing equipment and to the operation thereof it will be recalled that there is provided for each trunk line a switching device K located at the office X and a similar switching device K located at the ofiice Y. Each of these switching devices comprises an upper and lower row of individual switches. The normal contacts of the upper individual switches of the switching device K2 associated with trunk line L2, connect the signal control leads A2, B2 and G2, with the allotted contacts on the a, b and first to sixth levels of the automatic selector switch H; the signal receiving lead E2 with the upper normal contact of the pyramid selecting relay 81; and the starting lead ST with the start magnet 28 of the selector switch. The normal contacts of the lower individual switches of the switching device K connect the individ ual signal receiving relay and normally open signal initiating keys M2 and N2 of the testing equipment TE with the duplicate receiving and sending equipment DRE and DSE respectively.

In a similar manner, the individual switches of the switching device K2 associates the signal control, receiving and start leads of trunk line L2 at the oilice Y with the sending equipment SE and the upper normal contact of pyramid selecting relay 81, and also associates the signal receiving relay D2 and the signal initiating keys M2 and N2 with the duplicate receiving and sending equipment DRE and DSE'. In like manner, other switching devices K and K associate the signal control, signal receiving and start leads with the regular sending and receiving equipment, and the testing equipment thereof with the duplicate sending and receiving equipment.

Assuming that it is desired to test the selector switch H, the sending distributer TD and the receiving distributer RD to determine whether this apparatus functions prop erly when sending code signals corresponding to all trunk lines to which this appara tus is common, all switching devices K and K are actuated to open normal and close alternate contacts of their individual switches. The opening of the normal contacts of the upper individual switches disconnects the signal control, signal receiving and start leads associated with the individual trunk lines from the selector switches and receiving distributers. associated with the common signaling path P, while the closure of the alternate contacts of these particular individual switche connects these leads with similar duplicate sending and receiving equipment associated with the duplicate common signaling path DP. The opening of the normal contacts of the lower individual switches disconnects the signal initiating keys and signal receiving relays of the testing equipment for the individual trunk lines from the duplicate sending and receiving equipment associated with the duplicate common signaling path DP, while the closure of the alternate contacts of the lower individual switches connects the testing equipment with the sending and receiving equipment associated with the common signaling path P.

The signal initiating keys M at the oflice X individual to the trunk lines are then actuated one after the other in a definite predetermined order and if the signal lamps O at the office Y light in the same predetermined order it is known that the code signals were correctly set up at the ofiice In, transmitted over the signaling path P and received and translated at the office Y. Upon actuation each signaling initiating key M is held actuated until the signal lamp 120 common to these keys is lighted by the energization of its controlling relay 119. The lighting of this common lamp indicates to the testing operator that the correct code combination determined by the actuated signal initiating key has been set up and that this code combination is being transmitted by the sending distributer. Upon the restoration of an actuated signal initiating key M to normal position after the lighting of the lamp 120, relay 119 releases extinguishing the lamp 120. For further determining the correctness with which the equipment functions the two signal initiating keys for the various trunk lines at the oilice X are actuated simultaneousl and in a definite predetermined order. 5f the equipment is functioning properly the lamps O at the oilice Y will be extinguished in the order in which the pairs of signal initiating keys are actuated. Each pair of keys is held actuated until the associated common lamp 120 lights, when the keys are restored to normal position extinguishing the lamp.

What actually takes place when one of the signal initiating keys is actuated will now be described. In this description, the results of the actuation of signal initiating key M2 for trunk line L2 will be considered. The actuation of this key M2 causes the energization of start magnet 28 over circuit from battery through the winding of start magnet 28, common start lead ST, alternate contact of the lower individual switch 110,

left-hand normal contact of signal receiving relay 119 and the lower contact of signal initiating key M2 to ground. .Start magnet 28 in operating closes the operating circuit of the motor magnet MM, which thereupon advances the brushes of the se lector switch H until brush a engages one of its associated contacts which is grounded by the actuation of the signal initiating key M2. Relay 35 thereupon operates over a circuit from .battery over the left-hand winding of relay 35, brush a, alternate contact of the lower individual switch 111, upper contact of signal initiatingrkey M2 and the right-hand normal contact of signal receiving relay 119. Relay 35 immediately opens the operating circuit of the motor magnet MM which prevents the further advance of the brushes of the selector switch H. The closure of the middle alternate contact of relay 35 causes the operation of signal receiving relay 119 over a circuit from battery through the right-hand winding of relay 119, middle contact of the signal initiating key M2, alternate contact of the in dividual switch 112, contact engaged by brush b,middle alternate contact of relay 35 and the contacts of slow release relay 89 and release relay 37 to ground. Signal receiving relay 119 .upon being energized instantly completes a locking circuit from battery through its left-hand winding and left-hand alternate contact and the lower contact of signal initiating key M2 to ground. The lamp 120 is lighted in parallel with the locking winding of this relay 119. The lighting of this lamp indicates to the testing operator at the oflice X that the start relay 35 which controls the energization of the release magnet TDM ofthe sending distributer TDhas been energized so that the operator may thereupon restore the signal initiating key M2 to its normal position, whereupon signal receiving relay 119 is deenergized and releases its armature extinguishing the lamp 120. Atthe time relay 119 operated the opening of the normal contacts thereof opened theenergizing circuits of the start magnet 28 and the start relay 35. Upon the opening of these energizing circuits, start magnet 28 releases its armature but start relay 35 remains energized due to the locking circuit established through its right-hand winding upon its energization' Alfter the lighting of the lamp 120, the signalinitiating key may be restored to normal position'releasing relay 119, extinguishing the lamp'120 and disconnecting relay-i119 from the contacts of the selector switch H.

The brushes 1, 3. 4 and 6 of the switch H now connect positive battery 'with the respective individual sending segments 1, 3, 4e and 6 of the sending distributor TD. Positive battery is connected with the sixth gization of the release magnet TDM of the sending distributor TD. The sending distributer TD thereupon functions in the manner hereinbefore described to transmit over the common signaling path P, a code signal comprising six impulses, the first, third, fourth and sixth of which are positive and the second and fifth negative. After the transmission o f this code signal the sending distributer TD is restored to normal condition together with the control apparatus thereof, start relay 35, slow release relay 39 and release relay 37 If the receiving equipment is in proper working order, the reception of this trans mitted coded signal at the office Y, by means of the differential polarized relay 50, causes this relay to cooperate with the receiving distributor RD, whereupon, during the rotation of the brush arm of this receiving distributer, relay 58 is released, locking relays 62 and 65 are energized and locked up. The energization of locking relay 62' causes the energization of pyramid selecting relays to 73 inclusive. The pyramid selecting relays thereupon cooperate with the energized locking relay 65 to select the signal receiving lead 172. As the brush arm of the receiving distributer RD engages the segments 56 and 57 thereof a negative impulse of signaling current is transmitted over the selected signal receiving lead E2, through the alternate contact of the lower individual switch 11a and the right-hand winding of signal receiving relay D2 to ground. Signal receiving relay D2 upon being energized, completes a locking circuit from battery through its left-hand winding and left-hand contact to ground. This relay in closing its right-hand contact causes lamp 0'2 to light, indicating to the testing operator at the ofiice Y that the transmitted code signal has been properly received. With the brush arm of the receiving distributer RD returned to normal position, relay 58 is energized, causing the deenergization of locking relays (52 and 65 whereupon pyramid selecting relays 70 to 73' are deenergized. The receiving equipment is then in normalcondition.

'li hat actually takes place in the system when an associated pair of signal initiating keys are actuated, for example keys M2 and N2 individual to trunk line L2, will now be considered' The actuation of the signal initiating key M2 causes the control apparatus of the selector switch H to function in the manner hercinbefore described, while the actuation of the signal initiating key I 113 with the allotted contact of the sixth level of the selected switch. Start relay 35 is energized as before described when brush a engages the Contact grounded by the actuation of key M2, stops the motor magnet MM and causes the operation of the signal receiving relay 119, which serves the same purpose as when signal in tiating key M2 alone is actuated. The operation of the start relay 35 causes the sending distrihuter TD to function as before to transmit over the common signaling;- path I a code signal of six impulses, the fir t. third and fourth of which are positive and the second, fifth and sixth negative.

This code signal being office Y, the receiving distr the diiierential polarized rela received the Lbuter RD and y 50 cooperate to select the receiving lead E 2, and to cause the energization and locking: up of locking pole changing relay 66' which determines the polarity of signaling impulse to be transmitted over the selected ial receiving lead E2. Upon the engagement of the brush arm with segments 56 and 57 of the receivin; distributer RD positive. si naling current is connected with the right-hand winding of the signal receiv j relay D2 over a circuit from posi ive very through the upper normal contact of: relay 86', lower alternate contact of pole cha -n5; rel y 6 3, lower normal contact of relay 88-,

lo mal contact of relay 87, lower alternate contact of locking relay 05, upper normal contact of relay 87, lower normal contacts of relays 6'7 and (59. lower alternate contact of relay 73, upp normal contact of relay 81, signal recer lead E"2, alternate contact of individual switch 11% and the right-hand winding of signal receiving relay D2 to ground. This signal receiving relay D2 is similar to signal receiving relays 100 and 10 1 and when locked up is rendered dii'lerential by the transmission of a positive impulse through its right-hand winding. The signal receiving relay D2 therefore releases its armatures opening the circuit or and extinguishing the lamp 0'2.

If the improper code signal is set up by the actuation of any signal initiating key M at the oliice X, the lamp of the testing equipment at the oiiice Y will not be lighted. The testing operator at tie otlice X will be so advisec, and steps will be taken to locate and clear the trouble. It will be apparent, of course, that the sending and receiving equipment SE and BE may he similarly tested by first actuating the signal initiating keys M of the testing equipment TE at the 015% Y in a predetermined order to light the lamps O in the testing equipment TE- at the office X, and then simultaneously actuate the associated pair of signal initiating keys M and N in a predetermined order to extinguish the lamps 0.

Speed checking.

For the purpose of determining whether the sending and receiving distributors TD and RD at the opposite ends of the common signaling path P operate in synchronism, there is provided at the ofiice X a key 122 which cooperates with the sendin distributer TD, a key 121 at the office which cooperates with the receiving distributer RD and a plurality of signaling lamps 131 to 136, inclusive, as will more fully hereinafter appear. These keys, the signal lamps and the distributers cooperate with the testing equipment TE, the automatic selector switch H and the locking relays 61 to 66' in checking the speed of the distributers.

When it is desired to check the speed of the sending and receiving distributors TD and RD, the testing operators at the two offices actuate the switching devices K and K to associate the trunk lines with the duplicate sending and receiving equipments and the duplicate common signaling path DP and to associate the sending and receiving equipment of the common signaling path P with the testing equipments TE and TE. The testing operator at the office X then act-uates key 122 which is preferably of the locking type. The actuation of this key energizes the release magnet TDM which permits the free rotation of the brush arm of the sending distributor TD. The testing operator at the office Y actuates key 121 which is also preferably of the locking type. The actuation of this key energizes the release magnet RDM which permits the free rotation of the brush arm of the receiving distributor RD. The actuation of the key 121 also energizes relays 86 to 89', inclusive, disconnecting the pyramid selecting relays 67 to 81 and their associated circuits from the contacts of the locking relays 61 to 66' and connects therewith the signaling lamps 131' to 136, inclusive. The sending and receiving equipments associated with the common signaling path P are now in condition for checking the speed of the sending and receiving distributers TD and RD.

The operator at the oflice X now actuates one of the individual signal initiating keys M, for example, key M1 (not shown), which causes the control apparatus of the automatic selector switch H to function to advance the brushes of this switch until brush (1!. thereof engages the contact grounded by the actuation 6f the signaling initiating key M1, whereupon the brushes are stopped in this position. By reference to the table of signals, it will be observed that for trunk line L1, negative signaling current is connected with the third individual sending segment of the sending distributer TD,

while positive signaling current is connected with the first, second, fourth, fifth and sixth individual sending segments. Therefore, during each revolution of the brush arm of the sending distributer TD, a negative impulse will be transmitted over the common signaling path P when the brush arm engages the individual sending segment 3. Since the brush arms of the sending and receiving distributers TD and RD may not be released at the same time, these brush arms may not, of course, be rotating in phase although they may be in synchronism. So that at the time the negative impplse is sent over the common signaling path from the individual sending segment 3 of the sending distributer TD, the brush arm of the receiving distributer RD may be engaging any one of its six individual receiving segments-1 to 6, inclusive. If the brush arm of the receiving distributer RD engages individual receiving segment 5 when the negative impulse is transmitted over the common signaling path P from the individual sending segment 3 of the sending distributer TD, then looking relay is energized and locks up through its upper alternate contact and the contact of relay 58 to ground. The signal lamp 135' controlled by this locking relay is therefore lighted. The relay 65 will remain locked up and the lamp 135 controlled thereby will be lighted until the brush arm engages ring 52, and segment 55 of the receiving distributer RD, whereupon relay 58 energizes, releasing the relay 65 and extinguishing the lamp 135. If this signal lamp 135 is lighted during each revolution of the distributors, then the distributers are in synchronism.

However, should first one and then another of the group of signal lamps 131' to 136 inclusive, be lighted during the continued rotation of the brush arms, the testing operator knows that the distributers are not in synchronism. When not in synchronism, the order in which these lamps light indicates to the testing operator which of the two brush arms is being rotated more rap idly than the other. For example, should the lamps be lighted in the order of their numbers then the brush arm of the receiving distributer RD is moving faster than that of the sending distributer TD, while if in the reverse order, then the brush arm of the receiving distributer is moving slower than that of the sending distributer. The testing operator then proceeds to make the necessary adjustments to bring them in synohronism, which is indicated by the continued lighting and extinguishing of the same lamp. After the operation of checking speeds of the distributers is concluded, the system may be restored to its normal position by the restoration of keys 121 and 122. signal initiating key M1 and switching devices K and K to their normal positions.

What is claimed is:

1. In a telephone system, in combination, a plurality of trunk lines and a signaling path common thereto extending between two stations, means at one station for transmitting over the signaling path code signals, individual to the different trunk lines, each code signal comprising a plurality of current impulses, means common to the trunk lines for determining the character of some of the impulses of each code signal, and means individual to each'trunk line and controlled thereby for determining the character of another of the impulses of each code signal.

2. In a telephone system, in combination, a plurality of trunk lines and a signaling path common thereto extending between two stations, means at one station for transmitting over the signaling path code signals, individual to the'different trunk lines, each code signal comprising a plurality of current impulses, a code-determining switching device common to the trunk lines for determining the polarity of some of the impulses of each code signal, and a pole-changing relay individual to each trunk line and controlled thereby for determining the polarity of another of the impulses of each code signal.

3. In a telephone system, in combination, a plurality of trunk lines and a signaling path common thereto extending between two stations, means at one station for transmitting over the signaling path code signals individual to the different trunk lines, each code signal comprising a plurality of current impulses, means individual to each trunk line and controlled thereby for determining the character of one impulse of each code signal, and a switching device common to all and controlled by each of the trunk lines for determining the character of the remaining'impulses of each code signal. I

4. In a telephone system, in combination a plurality of trunk lines and a signaling path common thereto extending between two stations, means at one station for transmitting over the signaling path code signals individual to the different trunk lines, each code signal comprising a plurality of current impulses, a pole-changing relay individual to each trunk line and controlled thereby for determining the polarity of one impulse of each code signal, and a switching device common to all and controlled by each of, the trunk lines for determining the polarities of the remaining impulses Of each code signal.

5. In a telephone system, in combination, a plurality of trunk lines and a. s gnaling path common thereto extending between two stations, a sending distriluiter having individual sending contacts for transmitting over the signaling path code signals individual to the different trunk lines and co 1 prising current impulses equal in nun r to the number of individual sending contacts, a switching device havin sets of sta tionary contacts and a cooperating movable contact for each set connected with the lllfll: vidual contacts of the sending distributor for determining the character of the impulses of each code signal, and means individual to each trunk line and controlled thereby for determining the character 01 current connected with the stationary contacts associated with one of the movable contacts.

6. In a telephone system, in combination, a plurality of trunk lines and si,,., nc, ,ng path common thereto extending between two stations, a sending distribute! having individual sending contacts for transmitting over the signaling path code signals indiv' v. to the different trunk lines and 00111791 a plurality of current impulses equal in number to the number of individual sending contacts, a selecting switch. common to all and controlled by each of the trunk lines and comprisin a set of movable contacts connected with the individual contacts oi? the sending distributer and a plura ty of stationary contacts cocperatin with each movable contact for determin the polarities of the impulses of each signal, and a pole-changing switch ind dual to each trunk line and controlled thereby for determining the polarity of current connect ed with the stationary contacts coil-perating with one of the movable contacts.

7. In a telephone system, combine a plurality of trunk lines and si.- path common thereto extending between stations, means at one station for tin, ting over the signaling path code individual to the different trunk lines, cach code signal comprising a plurality of current impulses, a switching d ice llIYlllg' movable contacts and a plurality cooperating stationary contacts for each movable contact for controlling the code of the sim nals transmitted by the sending means, means responsive to each change in condition of one of the trunk lines tor causing the movable contacts to engage the same stationary contacts, and means external to the switching device and responsive to changes in the trunk lines for varying the code of the signal to be transmitted.

8. In a telephone system, in combination, a plurality of trunk lines and a signaling path common thereto extending between two stations, means at one station for transmitting over the signaling path code signals individual to the different trunk lines, each code signal comprising a plurality of current impulses, an automatic selector switch inn- 11 to the trunk lines and comprising a p urality of movable contacts and a plu- V of cooperating stationary contacts for car 1 movable contact for controlling the e do of the signals transmitted by the sendmeans, means for causing the engageitof movable contacts with the same erating stationary contacts upon each hange in condition of one of the trunk 1 es, and means individual to the one trunk to and responsive to changes in c0ndition thereof for varying the code of the signal to be transmitted.

9. In a telephone system, in combination, olurality of trunk lines and a signaling tions, a signal sending device at one stafon having individual contacts for transmitover the signaling path code signals inca 'lual to the different trunk lines, each code nal comprising a plurality of current impulses equal in number to the number oi? individual sending contacts, a switching device common to the trunk lines comprising sets of stationary contacts and a coo erating movable contact for each set of st ionary contacts, sources of positive and gative signaling current connected with the ario stationary contacts in predeterier for determining the polarities nt connected with all but one of the V l sending contacts of the sending Lrihuter, and pole-changing switches inividual to the trunk lines for determining larity of current connected with the nine individual sending contact of the n: distri outer.

J) In a telephone system, in combinac plurality of trunk lines and a signalcommon thereto extending between :tations. a sending device at one stat-ion nsmitting over the signaling path code p als individual to the different trunklines, a switching device common to the trunk lines ,on nrising stationary contacts divided oups each containing one contact for 'i runk line and a cooperating movable er itact for each group, means controlled by change in condition of any one of the .i lines for causing each movable cont to come to rest in engagement with its cooperatingstationary contact individual to the controlling trunk line. and means individual to and responsive to changes in condition oi the controlling trunk line and cooperating with the individual contact of one group for determining the code of the signal to be transmitted.

11. In a telephone system, in combination, plurality of trunk lines extending between two stations, a common signaling system for the trunk lines comprising a signaling path extending between the stations and'means at each end of the signaling path for transmitting and receiving thereover code signals individual to the different trunk lines, a duplicate common signaling sytem, means for testin each common signaling system, switching devices normally maintaining the first-mentioned common signaling system in operative relation to the trunk lines and the testing means in operative relation to the duplicate signaling system, and means for actuating the switching devices for disconnecting the first-mentioned signaling system, from and connecting the other signaling system with the trunk lines and for simultaneously disconnecting the testing means from the second and connecting it with the first signaling system.

12. In a telephone system, in combination, a plurality of trunk lines extending between two stations, signal-initiating means for the trunk lines at one station; signaling means common to the trunk lines comprising a signaling path extending between the two stations, means for transmitting the signals initiated by the trunk lines into code signals individual to the initiating trunk lines and for transmitting the code signals over the common signaling path, means at the other station for receiving and translating the transmitted code signals into signals inclividual to the initiating trunk lines; testing means comprising signal-initiating means at the one station, and signal-receiving and signaling devices therefor at the other station; and switching apparatus for disassociating the signaling means from the trunk lines and associating the signaling means with the testing means.

13. In a telephone system, in combination, a plurality of trunk lines extending between two stations, signal-initiating means for the trunk lines at one station; signaling means common to the trunk lines comprising a signaling path extending between the two stations, means for translating the signals initiated by the trunk lines into code signals individual to the initiating trunk lines and for transmitting the code signal over the common signaling path, means at the other station for receiving and translating the transmitted code signals into signals individual to the initiating trunk line; and testing means for the signaling means comprising keys at one station for initiating the same signals initiated by the signal-initiating means of the trunk lines for controlling the code signal translating and transmitting means, a signaling device at the one station responsive to the operation of the translating and transmitting means, and a signal control relay at the other station responsive to the transmitted codesignal.

14. In a telephone system, in combination, a plurality of trunk lines extending between two stations, signal-initiating means for the trunk lines at one station; signaling means common to the trunk lines comprising a sig naling path extending between the two stations, means for translating the signals initiatcd by the trunk lines into code signals individual to the initiating trunk lines and for transmitting the code signals over the common signaling path, means at the other station for receiving and t'anslating the transmitted code signals into signals individual to the initiating trunk lines; and testing means for the signaling means com prising pairs of keys equal in number to the number of trunk lines for initiating the same signals initiated by the signal-initiating means of the trunk lines whereby the code signal translating and transmitting means are controlled by each pair of keys, and a si 'nal control relay at the other station energized in response to a transmitted code signal upon the actuation of one key of a predetermined pair and de'e'nergized in response to another transmitted code signal when both keys of the same pair are actuated.

15. In a signaling system, in combination, a plurality of trunks extending between two stations, a signaling path common to said trunks, distributing means at each of the stations, signaling means at one station associated with the distributing means thereat and responsive to a predetermined permutation of impulses transmitted by the other distributing means when said distributing means are in unison, other signaling means at the one station common to said trunks and associated with the distributing means thereat and responsive to a like permutation of impulses transmitted by said other distributing means when the associated distributing means is leading the other and still other signaling means at the one station common to said trunks and associated with the distributing means thereat and responsive to a like permutation of impulses transmitted by the other distributing means when the associated distributing means is lagging behind the other.

16. In a signaling system, in combination, a plurality oi trunks extending between two stations, a signaling path common to said trunks, a rotatable sending distributer at one station, a rotatable receiving distributor at the other station, and signaling devices common to said trunks and associated with the receiving distributor and selectively responsive to like predetermined permutations of impulses transmitted by the sending dis tributer depending on whether the distributors are rotating in unison or whether the receiving distributer is loading or lagging behind the sending distributor.

17. In a signaling system, in combination, a plurality of trunks extending between two stations, a signaling path common to said trunks a rotatable sending distributor at one stat-ion, a rotatable receiving distributer at the other station, a signaling device associated with the receiving distributer and responsive to a predetermined permutation of impulses transmitted by the sending distributer when the two distributers are rotating in unison, a second signaling device common to said trunks and associated With the receiving distributer and responsive to a like permutation of impulses when the receiving is leading the sending distributer, and a third signaling device common to said trunks and associated with the receiving distrililuter and responsive to a like permutation of impulses when the receiving is lagging behind the sending distributor.

In Witness whereof I hereunto subscribe my name this 17th day of September A. D.,

WILLIAM L. DODGE. 

